1. Field of the Invention
The present invention generally relates to formulated resin systems, electronic circuit assemblies coated with such systems, and to methods for applying same.
More specifically, the present invention relates to protective polymeric films such as two part polyurethane resins for flood coating or encapsulating electronic circuit assemblies and other electronic devices that are part of a unitized construction, and which are susceptible to extreme environmental and/or mechanical degradation such as from vibration.
2. Description of the Related Art
There are a large assortment of two component filled or unfilled polymeric resin systems for potting and/or encapsulating of electrical circuit assemblies or other such electronic devices. Many of these formulations are based on similar technology using many of the same base raw materials to achieve desired properties during processing and/or at cure. The formulations are usually made up such materials as acrylic, polyurethane, silicone, or epoxy synthetic resins.
The main objective of a potting material is to provide protection and support of sensitive electronics in environments including exposure to chemical, high humidity, vibration, and temperature extremes. While these potting materials are successful, there is a need to reduce the weight and cost of such electronic assemblies. Potting materials are traditionally used to fill the device or assembly and, thus, are very thick. This feature can be considered disadvantageous for certain applications. Potted objects are also not easily re-enterable (i.e., soft enough to cut into for ease of removal for inspection and/or repair of the filled component). Accordingly, low hardness (soft), low modulus (elastic), vibration dampening polyurethane and silicone potting and encapsulation systems have been identified as the most desired materials for providing environmental protection and mechanical support of surface mount electronics that are subjected to such temperature extremes, as well as some level of vibration.
To this end, various manufacturers of electronic assemblies have chosen to use dielectric conformal coatings as their environmental protection barrier. Such conformal coatings are typically 2 mils (±1 mil) in thickness. Although this approach has proven successful in certain applications where a static environment exists, applications requiring mechanical support and environmental protection of large components exposed to temperature extremes and vibration have proven unsuccessful due to fatigue failure over time. The use of lead-free solder in electronic components has also contributed to the need for greater mechanical support and vibration dampening of large heavy electrical components.
The following U.S. Patents or Published Applications address some of the design challenges discussed above: U.S. Pat. Nos. 4,300,184; 5,863,597; 5,871,822; 8,360,390; and US2006/0076047.
Therefore, in an effort to fill the gap between thick and costly potting compounds and thin dielectric conformal coatings with little mechanical integrity, low hardness, low modulus formulated resin systems that are capable of providing mechanical structural support while providing vibrational dampening and reducing the overall resin weight and cost used in a conventionally potted assembly would be a useful advance in the art and could find rapid acceptance in any industry where use of potting and/or conformal coating systems are required.